In the oil and gas exploration and production industry, subsurface hydrocarbon-bearing rock formations are accessed by bores drilled from surface. The drilled bores are lined with tubular members, conventionally metal tubing known as casing or liner; for brevity, reference will be made primarily herein to casing. The casing is typically cemented in the bore by passing a cement slurry up between the annulus between the casing and the bore wall.
Any drilled bore will typically extend through a variety of formation types having different properties, for example formations which may swell after drilling to restrict the bore diameter, due to the chemical interaction with the drilling fluid. Also, when drilling between formations of different hardness, it is common for a ledge to be created at the transition between the formations. Further, in deviated or horizontal bores, drill cuttings can fall out of mud suspension and will often collect on the low side of the bore, to form cuttings beds. If the cuttings are not cleaned from the bore, the presence of the cuttings makes successful running in and cementing of casing more difficult and in some cases impossible. In an effort to overcome these difficulties, a length of casing may be provided with a shoe at its leading end, which shoe may include numerous features, including cutting blades, an eccentric or offset nose, jetting ports and like, all intended to facilitate progress of the casing past obstructions in the bore. To minimise the drag between the casing and the bore wall as the casing is run into the bore, and also to facilitate rotation of the casings as it is run in and during cementing, casing strings are often provided with centralisers at various points along the length of the string. Centralisers are conventionally annular, to permit mounting on the casing, and feature upstanding spaced apart blades which allow fluid and cement passage.
It is among the objectives of the various aspects of the present invention to provide centralisers and other apparatus to facilitate the running in and cementing of casing and other tubulars.